798

THE COLLIERY GUARDIAN.

April 18, 1913.

more than doubtful that that diminution of oxygen could
be physiologically endured by men engaged in hard work.
He had, on more than one occasion, had to exert himself in
an atmosphere deficient in oxygen, and the increased
breathing was too distressing to make it possible to admit
that it could be daily endured in mines for the purpose of
ordinary toil.

Physiological Effect of Nitrogen.

Dr. Harger contended that, provided a man breathed the
same weight of oxygen, it did not matter how much
nitrogen there might be with it. In other words, a man
might, with equal benefit, breathe 17£ per cent, of oxygen
at sea-level as 21 per cent, at an altitude of 5,OOOft., because
in each case there was exactly the same weight of oxygen.
In such circumstances a lamp would not burn at the sea-
level, but it would burn on the mountain, so that, according
to Dr. Harger, while combustion would fail in a lamp it
would not at all fail in a man. Mr. Blackett wanted to
know on what ascertained physiological grounds such an
assertion was made.

Men who had to live and get their living in the mines
would want more solid proof than mere assertion or the
evidence of a comparatively short period of experiment.
The speaker was very ignorant of physiological chemistry,
but he failed to see how the two conditions above assumed
could be “ exactly alike ” for respiration. If the nitrogen
were so thick at sea-level that it prevented the lower
percentage of oxygen from burning at the candle, might it
not also detrimentally affect proper physiological action
through the lung cells ? Man’s lungs had been evolved
through countless thousands of years to deal with 21 per
cent, of oxygen by volume; and, whether that volume
contained more or less condensed air, the molecules of
oxygen had always to meet the same number of molecules
of nitrogen, and their relative effect was always the same;
but, if the oxygen molecules had more nitrogen molecules
to encounter, how could the results be the same ? Seventeen
and a-half parts of oxygen among 82| of nitrogen could not
have the same freedom of effect as when these 17| parts
were amongst only 66 of nitrogen. The liberties of the
subject were being very much curtailed in mines nowadays,
but the speaker did humbly hope and pray that they might
be allowed to continue the use of ordinary unpatented air
for breathing.

Concussive Waves.

As to other preventives of explosions, it was quite possible
that there were expedients which, in certain circum-
stances, would prevent ignition, but these had not yet been
tested, and would be unnecessary if incombustible dust were
used, on the principle that the greater contained the less.
It would, he believed, be eventually proved that, without
any concussive wave in the air, a large body of flame would
be required to fire coaldust, while much less flame would
suffice if there were also a wave. In shot-firing, for
instance, the shot-hole or other direction of relief for the
explosive would have to be aimed at a store of fine coaldust
in order to raise it in suspension in time to receive some
projected vagrant flame and a concussive wave all exactly
at the same critical moment. If the shot-hole happened to
be in such a position in a gallery as to favour the reflection
of one wave on top of another, so that two crests
coincided at the critical moment, there would then exist a
condition more favourable to ignition. It was quite possible
that the crest of a wave from mechanical propulsion might
disastrously coincide with the crest of a sound wave or
both with another reflected from the shape of the gallery,
when a still more favourable condition would be set up.
Obviously, then, if any of these coincident necessities were
to fail or be prevented, there might be no ignition. Of course
the whole chain would fail always if the dust were not
capable of ignition, and it would be quite easy to " wet ”
the surroundings of a shot by means of incombustible dust
as by water. The laying down of incombustible dust near
a shot or the wetting of its surroundings with water was
equivalent to covering the coaldust with a carpet and so
preventing it from rising. Why not, then, cover the dusty
neighbourhood a few yards in front of a shot with a carpet
of, say, brattice cloth ? He prophesied that experiments
would show that that expedient would frustrate ignition if
it could be established that ignition would otherwise be
certain—not quite so easy as some people thought.

In all these cases the coaldust menace only had been
killed, which was enough; but might not some of the
other “ ingredients ” be killed also ? It might be possible
that a brattice-cloth screen could be so hung that it would
cut off the flame from the coaldust raised, but, what seemed
equally important, it might also muffle or cut off some of
the dangerous air-waves. All these points might be very
difficult to demonstrate. It should not be forgotten, how-
ever, that there was now the incombustible dust to be going
on with, and, mixed with brains, it should prevent, if not
all, at least a very large proportion of occurrences which
might otherwise become colliery explosions.

There were coincident possibilities of the creation in
collieries of conditions favourable to explosions which it was
difficult to deal with otherwise than by incombustible dust.
He instanced the heavy fall of roof, which might at once
create at least two of the dangerous conditions—a thick
cloud of dust and a wave. Without the wave it would
probably ignite only at a large flame, but with the wave he

recently ? This only—and with it must always be associated
the name of Dr. W. E. Garforth—that, if there was not
sufficient incombustible dust present already in the galleries
to prevent the ignition of the accompanying coaldust, it
was quite feasible and common-sense to put it there in such
positions as would more easily conduce to its being raised
into the air. The fact that the idea was taking hold of
increasing numbers of coalmining men was of tremendous
importance.

It was strange to find how great a difficulty many colliery
officials had in grasping the ease of application of that
preventive. They had no difficulty whatever in coming to
an understanding about water, but with dust it seemed
quite another thing—whereas, in principle, the two might
be looked upon in exactly the same light. If water were
poured on fire, the flame was put out; if dust were poured
on fire, the same thing happened. If coaldust were
moistened with water, it could not be inflamed; if with
stonedust, there was the same effect—with the important
difference that coaldust wetted with water would dry again,
butt( wetted ” with stonedust it would be safe for ever.

Shaledust and Fluedust,

By the rapid absorption of heat, both water and incom-
bustible dust became quenching agents and acted as
oxygen-excluders. All material when heaped up formed a
natural angle of repose, and, therefore, if incombustible
dust already occupied either natural or artificial spaces at
that angle, there could be so little room left for a subse-
quent coating of coaldust as to render its presence more or
less innocuous. He had used the term “ incombustible ”
because there were, at a great many collieries, large
quantities of suitable dust ready to hand in the burnt dusts
which had been removed from the boiler main flues and
similar places. Experiments with shaledust and fluedust
had shown better results with the latter than with the
former, the latter being thrown more easily into the air by
the “ pioneering ” disturbance and having excellent
quenching properties. The qualities of fluedusts would,
however, vary according to the character of the fuel from
which they were derived. Certain siliceous dusts, when
present thickly and constantly in the air, had been found to
produce in workmen fibroid conditions of lung favourable
to tuberculous growths, and steps had had to be taken to
avoid that danger. It had been suggested that fluedust
was, for that reason, dangerous when used in mines, but
there were really no true grounds for such a contention.
There was no reason why it should be present in the air in
sufficient quantities to do harm, and those handling it, in
applying it to the roadways, could do so to the leeward of
the air-current.

If mines were made and maintained in that state of
incombustibility—and there seemed no reason why they
should not be—why could not many of the restrictions now
placed upon mines be removed ? Every colliery which put
its ways into such a state might be relieved of all restric-
tions applying to “ dry and dusty mines,” just as, at present,
a mine “ naturally wet throughout ” need not observe all
the restrictions of a dry mine. The glimpse of such a
Heaven-sent relief from off the shoulders of the present-day
manager groaning under the pitiless burden of recent legis-
lation was almost too dazzling, but it could not be said to
be other than possible.

Molecular Action of Oxygen,

Although there were so many legislating politicians and
some others who apparently thought that they knew all that
was worth knowing about collieries, mining engineers had
learnt something about their work and were aware that, to
effect inflammation and combustion of any ordinary kind,
oxygen was required. It was not difficult, even for mining
engineers, to grasp the elemental fact that the more closely
the molecules of oxygyen could be brought into contact
with the coaldust with which they were to combine, the
more easily that matter would inflame and the more rapid
would be the combustion. It had been demonstrated that,
as a dust “ explosion ” progressed in a pit, it was able, by
the pressure of its combustion, to build up conditions which
were more and more favourable to an increased intensity
of action, owing mostly to the compression of oxygen which
took place between the momentum behind and the reluctant
inertia of the air current in front. In a rough way it might
be said that the thicker the oxygen the more easy and
intense the combustion. The converse naturally applied.

There were many ways in which some thinning of
oxygen could take place, for, the pressure being reduced, a
shallow pit would be safer than a deep one and a low
barometer than a high one, or the room in the air for
oxygen molecules could be reduced by increasing the
quantity of nitrogen or other inert gas. Dr. John Harger
thought so highly of the latter idea that he had protected
it by patent, and lost no opportunity of recommending that
collieries should dilute their ordinary atmospheric air by
adding purified flue gases. At the risk of being pilloried
as one of a crowd of unenlightened experts who had been
running the mines for many 5 ears—a very unkind way of
describing mining men—the speaker disagreed with Dr.
Harger, and said that the latter's method was impracticable
in mining, for even if the production of inert gas in such
quantities as would sufficiently dilute the hundreds of
thousands of cubic feet per minute in the largest and most
dangerous mines were commercially possible, it was stil

thought a much less flame would suffice. The wave served
to knock the molecules together where more gentle impact
failed.

Matches and Electricity.

How many things were there at a colliery which could, by
a strange coincidence—the coincidence must be most extra-
ordinary—furnish a source of ignition for that condition ?
There was the menace of the discarded matches. How many
had been found, and how many there must be still remaining
hidden in all mines ! A forgotten box in the pocket—the
fear of prosecution, so strongly advocated by some members
of the Royal Commission—and the hiding of it in the pit.
A roller spindle might have run hot and set contiguous
dust smouldering just as the last“ set” of the day had been
run, until, hidden and unnoticed, the ventilating current
had fanned it into a flame at the most unlucky of all coinci-
dental moments. Then, there was the oft-suspected and
usually undeserving electricity, which might also furnish
the ignition. The coincidence in that case would be more
remote, however, because of the time element, as the main-
tenance of an arc and the blowing of safety fuses would be
but momentary occurrences, while the first named possibili-
ties of flame could last over a long time. He did not
think that small flames of lamps were at all a likely source
except through the medium of firedamp, for the pioneering
wind from the cause of the dust-cloud would probably blow
out such a small flame before its contact with sufficient dust
could have been possible. The whole effort of the miner
should be directed towards preventing the possibility of
coaldust ignition, and, when that was consistently done, there
would be no need to strain one’s mind in devising means for
the quenching of an explosion once started. The conditions
which would prevent ignition would be quite sufficient to
effect quenching, and all the talk of zones, water-screens,
automatic trip-quenchers and similar devices would die a
natural death. Once coaldust had been scotched, there
would be little need to fear firedamp, for the danger of the
latter was trivial in the absence of its more deadly ally.

Secondary Causes.

Although there had been much study as to the place of
origin and cause of ignition in colliery explosions—notably
by Messrs. W. N. Atkinson and A. M. Henshaw in their
pamphlet on “ The Investigation of Colliery Explosions ”—
there was still much to be learnt. While the driving force
of the rush from the initiating centre, and, also, its
radiating explosive violence, doubtless produced the chief
violence, there were, as was well known, very violent
secondary causes, and, as was not so well known, there must
be also many subsequent movements. The position, extent
and direction of the communicating galleries would largely
govern these, and there must also be numerous cases where
the “backlash” and “counter backlash”—to coin a new
term—instead of retraversing the paths of direct return to
the seat of cooling vacuum, would find themselves fore-
stalled by an inrush from other parts of the mine which
were nearer, and had found readier communication through
some blown-out doors or stoppings. The bounding and
rebounding due to air elasticity alone must also produce
many varying currents of diminished force. He had
counted as many as 16 oscillations in the experimental tube
at Eskmeals, several of which carried flame with them.

It was little wonder that the indications of force and
direction in a mine after an explosion were found at times
to be very bewildering and to require very great caution in
reading. Particularly was that the case in reconstructing
mentally the course of events from deposits of dust and
coke on props and similar surfaces. When the explosion
had driven in towards an expanded cul-de-sac to a district
of workings, where the air contents might be compressed,
the rebound to fill the pull of the vacuum on one side, while
being pushed by the compression on the other, must some-
times produce a comparatively more violent “ backlash ”
than where quite contrary conditions had prevailed, such as
out towards the open shaft. In the former case, there
would be a diminishing explosive force, due to weakened
“ pioneering ” and an increased “ rebound,” whereas, in the
latter case, the explosive force would be increasing but
have no push back from compression into gallery ends.
Dust-deposits were very deceiving at times. There might
be narrow bands, broad bands and coke bands, reversing
themselves in what appeared to be an unaccountable
manner, while, if by chance a still atmosphere prevailed
owing to a balance in pressure and the gallery was full of
the thick, oily smoke distilled from the combustion of coal,
there would be extraordinary deposits of thick, velvet-like
soot lying in a blanket on horizontal surfaces. On the
whole, while the narrow band of dust on a prop might mean
the more forcible propulsion of a dense coal-cloud in the
direction from the side of the band to the other side and
the broad band indicate a less violent reverse current, there
could not be much reliance placed upon either to indicate
the source of ignition until all other conditions had been
studied and brought into account. Coke was generally the
deposit of the hot, sticky coaldust in the heated returning
current, but not always, and might be deposited in a
different form by the original blast.

The Construction of Stoppings.

Mr. Blackett condemned, as a most serious and, probably
deadly provision, that portion of the Coal Mines Act which
provides for stoppings being so constructed as not to be